1. Field of the Invention
The invention relates to a method for recognizing or identifying the phase of the cylinders of a multi-cylinder four-stroke internal combustion engine, of the type equipped with an ignition system and/or fuel injection system controlled individually for each cylinder, and comprising a sensor, often called the crank angle sensor, which is fixed with respect to the engine and detects the movement past it of at least one position mark fixed on a rotary target which rotates integrally with the engine crankshaft, to supply a signal indicating the passage of the piston of a reference cylinder of the engine through a determined position, for example approximately 100.degree. crank angle before top dead center (TDC) for this piston.
2. Description of the Prior Art
To optimize the operation of a four-stroke internal combustion engine, particularly for controlling a sequential ignition system and/or a sequential multi-point fuel injection system of such an engine correctly, it is known that the phase of the cylinders of the engine needs to be identified or recognized, that is to say that at every moment during an engine cycle it is necessary to know the position of each of the various pistons of the engine as well as which phase or stroke of the engine cycle each of the various cylinders of this engine is performing, and in particular the passage of the pistons through the TDC position at the beginning of the induction phase, so that the moment at which fuel is to be injected can be defined with precision, and their passage through the TDC position at the beginning of the combustion-expansion phase, so that ignition (the moment and energy of ignition) can be defined with precision if the internal combustion engine is a controlled-ignition engine.
In effect, in an electronic and multi-point fuel injection system, which comprises at least one injector per cylinder for injecting metered amounts of fuel just upstream of the corresponding inlet valve or valves, and in which the injectors are operated periodically and at least once per engine cycle, sequential injection consists in operating the various injectors in turn and in a given order, so that the metered amounts of fuel can be injected toward the cylinders in the most favorable conditions relative to the corresponding induction phases. Likewise, a sequential ignition system allows ignition to be commanded in turn and in a given order in the various cylinders under the best conditions with respect to the corresponding combustion-expansion phases, that is to say, in practical terms, with an appropriate ignition advance, with respect to TDC, at the beginning of the corresponding combustion-expansion phase, as a function of the operating conditions of the engine, and does so without simultaneously causing an unnecessary and sometimes disturbing spark in another cylinder which is performing an engine stroke ill-suited to being fired.
Ignition systems and/or fuel injection systems of the sequential type for internal combustion engines generally comprise an engine control computer, which in particular manages ignition and fuel injection and which must, for this, always know which phase the cylinders are in so that it can precisely monitor the way in which the engine cycle is occurring in each of these cylinders so that the engine control computer can calculate and command the amount of fuel delivered by each injector, that is to say in actual fact the injection period, starting from a determined moment, on the one hand, and so that the engine control computer can calculate the moment of ignition and trigger it by commanding a corresponding ignition coil, on the other hand.
On a rotating target, that rotates integrally with the engine crankshaft or flywheel, and generally consists of a ring gear whose teeth, distributed about the periphery of the ring, constitute marks for measuring the rotational speed of the engine and the position of the crankshaft, by traveling past a sensor, for example a variable-reluctance sensor fixed on the engine, it is known to position at least one position mark which for example consists of a tooth and/or a gap which has a different width from the others, so that it forms a unique feature that can be distinguished from the other teeth and/or spaces which are uniformly distributed, so that regions with an angular position that correspond to a determined phase in the stroke of the pistons can be identified on the ring gear. By moving past the fixed sensor, the position mark generates a distinctive signal each time the pistons of the engine pass through a known fixed position, and this allows the engine control computer to calculate, among other things, the moments at which the various pistons pass through top dead center.
However, in a four-stroke internal combustion engine, one engine cycle corresponds to two revolutions of the crankshaft, which means that the piston of the reference cylinder during each engine cycle passes through TDC twice, but during two different phases of the engine cycle.
In particular, for engines with four in-line cylinders, numbered in turn from 1 to 4 from one end of the engine block to the other, the firing order for the cylinders is generally given by the sequence 1, 3, 4, 2 and the pistons of cylinders 1 and 4 pass simultaneously through top dead center alternately, one at the beginning of an induction phase and the other at the beginning of a combustion-expansion phase, while the pistons of cylinders 2 and 3 also pass simultaneously through TDC with a phase shift of half of an engine revolution as compared with cylinders 1 and 4, and like the latter cylinders alternately at the beginning of an induction phase and at the beginning of a combustion-expansion phase.
In consequence, it is known that it is not possible simultaneously to obtain information regarding the angular position and information regarding the phase of the various pistons of a four-stroke engine just using the signals resulting from the passage of position marks on a ring gear driven with the crankshaft past a sensor fixed on the engine, that is to say just from the signals given by a crank angle sensor which usually is also an engine speed sensor.
For appropriate control of a sequential ignition and/or sequential injection system, it is known to make use of additional information relating to the phase of the cylinders and which is given by a second sensor, possibly of the same type as the first one, for example a variable-reluctance sensor, and which is sensitive to the movement past it of marks, such as teeth, borne by a second rotary target, such as a ring gear driven in rotation at a speed which is half that of the crankshaft, so that this second target makes one full revolution per engine cycle. For this, it is known to make the second target rotate integrally with the distributor rotor shaft or, more frequently, the camshaft or its drive pulley. It is especially known for the second rotary target, driven with the camshaft, to bear a single position mark which interacts with the second sensor to deliver a signal that has two logic levels.
Thus, the interaction of the first sensor with the first rotary target gives the information on the angular position of the piston of a reference cylinder, while the interaction of the second sensor and the second target gives the information regarding the phase of this reference cylinder, for which reason the assembly formed by the second sensor and the second rotary target is generally dubbed engine-phase sensor.
However, the presence of two sensors and two rotary targets is a factor in increasing the cost and the size and the complexity of assembly.
In order to overcome these drawbacks, FR-A-2 692 623 proposes a method for identifying the cylinders which saves on having to have an engine phase sensor and replaces it with an analysis of engine torque, in order to detect misfires that are the result of a command to stop injecting fuel into a reference cylinder as the piston of this cylinder passes through TDC.
More specifically, this method for producing a signal for identifying the cylinders, comprises the following steps:
stopping injecting fuel for a given reference cylinder of the engine at a precise moment and for a precise length of time; PA1 observing, using the signal for detecting misfires, the occurrence of a misfire in the reference cylinder following the non-injection and the moment that the misfire is detected; PA1 calculating the number of TDCs separating the moment that injection is stopped in the reference cylinder and the moment the misfire resulting from this stoppage is detected, and identifying by deducing the moment of passage through TDC whether the reference cylinder is an induction or a power stroke; and PA1 formulating the cylinder identification signal, this signal, which is in phase with the TDC signal, being reset at the moment that the reference cylinder passes through TDC on an induction or power stroke and taking up the successive order of combustion in the cylinders. PA1 in commanding, on said reference cylinder and at a given moment that is associated with said piston of the reference cylinder passing through said determined position, a disturbance other than complete stoppage of command for the injection of fuel, and liable to cause variation in the engine torque, PA1 in observing the engine torque and detecting a possible variation in engine torque as a result of said command for disturbance on said reference cylinder, and in detecting the moment at which said variation in engine torque occurs or the absence of variation in engine torque, PA1 in examining the relationship between said given moment at which the disturbance is commanded and said detected moment that the variation in engine torque or said absence of variation in engine torque occurs, in order to deduce from this which phase of the engine cycle said reference cylinder was in when it passed through said determined position, and PA1 in recognizing the phase of all the cylinders of the engine on the basis of knowledge of the phase of the reference cylinder.
This method does however have the drawback that to use it assumes the presence not only of a crank angle sensor, for identifying the passage through TDC of the piston of a reference cylinder, but also of a system for detecting misfires, capable of supplying a signal allowing misfires that occur in the various cylinders to be identified.
Another drawback with this method is that it can only be used on an engine that is equipped with a fuel injection system controlled individually per cylinder, which means that it cannot be used on an engine equipped, for example, with a mono-point fuel injection system and a sequential ignition system.
The problem underlying the invention is that of overcoming the drawbacks of the method known from FR-A-2 692 623 and of proposing a method of recognizing the phase of the cylinders which can be employed on an engine that is equipped with a crank angle sensor, without a phase sensor or a system for detecting misfires, it being possible for the engine to have a fuel injection system that is controlled individually and/or an ignition system that is controlled individually per cylinder. Thus the method of recognizing the phase of the cylinders according to the invention can be used whether the ignition is sequential and with any kind of injection, for example mono-point, multi-point "full-group" (i.e. simultaneous injection into all cylinders) or semi-sequential, symmetric or semi-sequential asymmetric, or sequential and phased or alternatively sequential and unphased, or whether the injection is multi-point sequential and with any kind of ignition, for example static or twin static (that is to say producing sparks in two cylinders simultaneously for each engine half revolution).